Chemokines are chemotactic cytokines that are released by a wide variety of cells to attract macrophages, T cells, eosinophils, basophils and neutrophils to sites of inflammation (reviewed in Schall, Cytokine, 3:165-183 (1991), Schall, et al., Curr. Opin. Immunol., 6:865-873 (1994) and Murphy, Rev. Immun., 12:593-633 (1994)). In addition to stimulating chemotaxis, other changes can be selectively induced by chemokines in responsive cells, including changes in cell shape, transient rises in the concentration of intracellular free calcium ions ([Ca2+])i, granule exocytosis, integrin upregulation, formation of bioactive lipids (e.g., leukotrienes) and respiratory burst, associated with leukocyte activation. Thus, the chemokines are early triggers of the inflammatory response, causing inflammatory mediator release, chemotaxis and extravasation to sites of infection or inflammation.
There are four classes of chemokines, CXC(α), CC(β), C(γ), and CX3C(δ), depending on whether the first two cysteines are separated by a single amino acid (C-X-C), are adjacent (C-C), have a missing cysteine pair (C), or are separated by three amino acids (CXC3). The α-chemokines, such as interleukin-8 (IL-8), melanoma growth stimulatory activity protein (MGSA), and stromal cell derived factor 1 (SDF-1) are chemotactic primarily for neutrophils and lymphocytes, whereas β-chemokines, such as RANTES, MIP-1α, MIP-1β, monocyte chemotactic protein-1 (MCP-1), MCP-2, MCP-3 and eotaxin are chemotactic for macrophages, T-cells, eosinophils and basophils (Deng, et al., Nature, 381:661-666 (1996)). The C chemokine lymphotactin shows specificity for lymphocytes (Kelner, et al., Science, 266:1395-1399 (1994)) while the CX3C chemokine fractalkine shows specificity for lymphocytes and monocytes (Bazan, et al., Nature, 385:640-644 (1997).
Chemokines bind specific cell-surface receptors belonging to the family of G-protein-coupled seven-transmembrane-domain proteins (reviewed in Horuk, Trends Pharm. Sci., 15:159-165 (1994)) termed “chemokine receptors.” On binding their cognate ligands, chemokine receptors transduce an intracellular signal through the associated heterotrimeric G protein, resulting in a rapid increase in intracellular calcium concentration. There are at least twelve human chemokine receptors that bind or respond to β-chemokines with the following characteristic pattern: CCR1 (or “CKR-1” or “CC-CKR-1”) MIP-1α, MIP-1β, MCP-3, RANTES (Ben-Barruch, et al., J. Biol. Chem., 270:22123-22128 (1995); Neote, et al., Cell, 72:415-425 (1993)); CCR2A and CCR2B (or “CKR-2A”/“CKR-2A” or “CC-CKR-2A”/“CC-CKR2A”) MCP-1, MCP-3, MCP-4; CCR3 (or “CKR-3” or “CC-CKR-3”) eotaxin, RANTES, MCP; (Ponath, et al., J. Exp. Med., 183:2437-2448 (1996)); CCR4 (or “CKR-4” or “CC-CKR-4”) TARC, MDC (Imai, et al., J. Biol. Chem., 273:1764-1768 (1998)); CCR5 (or “CKR-5” or “CC-CKR-5”) MIP-1α, RANTES, MIP-1β (Sanson, et al., Biochemistry, 35:3362-3367 (1996)); CCR6 MIP-3 alpha (Greaves, et al., J. Exp. Med., 186:837-844 (1997)); CCR7 MIP-3 beta and 6Ckine (Campbell, et al., J. Cell. Biol., 141:1053-1059(1998)); CCR8 I-309, HHV8 vMIP-I, HHV-8 vMIP-II, MCV vMCC-I (Dairaghi, et al., J. Biol. Chem., 274:21569-21574 (1999)); CCR9 TECK (Zaballos, et al., J. Immunol., 162:5671-5675 (1999)), D6 MIP-1 beta, RANTES, and MCP-3 (Nibbs, et al., J. Biol. Chem., 272:32078-32083 (1997)), and the Duffy blood-group antigen RANTES, MCP-1 (Chaudhun, et al., J. Biol. Chem., 269:7835-7838 (1994)).
Chemokine receptors, such as CCR1, CCR2, CCR2A, CCR2B, CCR3, CCR4, CCR5, CCR6, CCR7, CCR8, CCR9, CXCR1, CXCR2, CXCR3, CXCR4, CXCR5, CX3CR1, and XCR1 have been implicated as being important mediators of inflammatory and immunoregulatory disorders and diseases, including asthma and allergic diseases, as well as autoimmune pathologies such as rheumatoid arthritis and atherosclerosis.
The CXCR3 chemokine receptor is expressed primarily in T lymphocytes, and its functional activity can be measured by cytosolic calcium elevation or chemotaxis. The receptor was previously referred to as GPR9 or CKR-L2. Its chromosomal location is unusual among the chemokine receptors in being localized to Xq13. Ligands that have been identified that are selective and of high affinity are the CXC chemokines, IP10, MIG and ITAC.
The highly selective expression of CXCR3 makes it an ideal target for intervention to interrupt inappropriate T cell trafficking. The clinical indications for such intervention are in T-cell mediated autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, and type I diabetes. Inappropriate T-cell infiltration also occurs in psoriasis and other pathogenic skin inflammation conditions, although the diseases may not be true autoimmune disorders. In this regard, up-regulation of IP-10 expression in keratinocytes is a common feature in cutaneous immunopathologies. Inhibition of CXCR3 can be beneficial in reducing rejection in organ transplantation. Ectopic expression of CXCR3 in certain tumors, especially subsets of B cell malignancies indicate that selective inhibitors of CXCR3 will have value in tumor immunotherapy, particularly attenuation of metastasis.
In view of the clinical importance of CXCR3, the identification of compounds that modulate CXCR3 function represents an attractive avenue into the development of new therapeutic agents. International Publication No. WO 02/083143, for example, describes CXCR3 antagonists. With the study of CXCR3 modulators, new developments and improvements been recognized leading to new compounds provided herein.